What Thickness Should a Bunk Bed Mattress Be?
There is a real number here, not a preference: EN 747-1:2024, the bunk bed safety standard most South African-made frames are built to, requires at least 160mm (16cm) of clearance between the top of the mattress and the top of the guardrail. That means the mattress thickness question has a formula, not a rule of thumb: guardrail height minus 16cm equals your maximum safe mattress thickness. Measure your guardrail before you buy, not after.
How to measure your guardrail
Stand at the top bunk. Measure straight up from the surface the mattress will sit on (the base or slats, not the floor) to the top edge of the guardrail. Write that number down in centimetres. That is the only measurement this formula needs.
The formula, worked through
| Your guardrail measurement | Maximum safe mattress thickness | Working |
|---|---|---|
| 40cm | 24cm | 40 minus 16 |
| 34cm | 18cm | 34 minus 16, matches our standard Comfort Foam Single |
| 31cm | 15cm (150mm) | 31 minus 16, matches our Bunk Bed Height Comfort Foam |
| 28cm | 12cm | 28 minus 16, thinner than either of our current builds |
If your guardrail measurement lands below 31cm, neither of our two current Comfort Foam heights is thin enough and you should not assume either fits safely. Speak to us before ordering rather than guessing.
Why we build to exactly two thicknesses
Our Comfort Foam Single comes in an 18cm standard build and a 150mm (15cm) Bunk Bed Height, both 50 kg/m3 SABS-approved foam, both R2,399, both carrying a 3 year warranty and the standard 365 night trial. The 150mm option exists specifically for guardrails between 31cm and 33cm, where the standard 18cm build would exceed the EN 747-1 clearance rule.
What this article is not
This is a single-purpose answer to one question: what thickness. For the full comparison across our mattress range, including density and price, read the full bunk bed mattress guide. For whether a normal, non-bunk-specific single mattress can ever be the right call, read can I put a regular mattress on a bunk bed.
Two worked examples, start to finish
Example A: a 36cm guardrail
You measure the top bunk and get 36cm from the base to the top of the guardrail. Subtract 16cm: 36 minus 16 equals 20cm. Any mattress up to 20cm thick is safe here, so our standard 18cm Comfort Foam build fits with 2cm to spare.
Example B: a 32cm guardrail
You measure again on a different bed and get 32cm. Subtract 16cm: 32 minus 16 equals 16cm. Our standard 18cm build is now too thick by 2cm, but our 150mm (15cm) Bunk Bed Height fits with 1cm to spare. This is the exact case the 150mm option was built for.
Why 16cm and not some other number
The 16cm figure in EN 747-1:2024 is not arbitrary. A guardrail's job is to present a physical barrier above the sleeping surface tall enough that a rolling or shifting sleeper is stopped before going over the edge. Too little clearance and the barrier's effective height (measured from where the child actually lies, not from the frame) becomes too short to do that job, even if the guardrail itself looks tall on the empty frame. The standard is written around the mattress surface, not the frame, precisely because that is where the sleeping child actually is.
A note on toppers
If you plan to add a mattress topper to a top bunk, measure your guardrail with the topper's thickness already added to the mattress. A topper genuinely adds height, and it is easy to push a compliant setup out of clearance by adding one without re-checking the arithmetic.
Frequently asked questions
What is the formula for bunk bed mattress thickness?
Guardrail height above the base, minus 16cm (the EN 747-1:2024 minimum clearance), equals your maximum safe mattress thickness.
Is there a South African standard for this, separate from EN 747-1?
No confirmed South African national standard (SANS) number exists for this specific measurement. EN 747-1:2024 is the reference most South African-made bunk frames are built to.
What if my guardrail measurement is below 31cm?
Neither of our current Comfort Foam heights (18cm or 150mm) is guaranteed to fit safely below a 31cm guardrail. Contact us before ordering rather than assuming.
Does adding a topper change the calculation?
Yes. Measure your guardrail with the topper's thickness already included in your mattress height, not just the bare mattress.
Related: Best mattress for bunk beds, the full guide · Can I put a regular mattress on a bunk bed · Landing page: both heights side by side
Reviewed by Andries Taljaard, Founder of Mr Mattress.